Caverns of large size for the storage of gases have been formed by washing out with water subterranean salt beds or strata. Since these caverns are located at considerable depth, for example, 1400 meters below the earth's surface, it is practically impossible to wash out completely the saline waters or brine that are thus left therein. Moreover, this sediment or brine cannot readily be removed therefrom except by costly technical means.
The sediment or brine which remains in the cavern consists essentially of a concentrated salt solution that has the undesirable property of humidifying, that is, wetting or moistening the stored gas, as a consequence of which the gas must be dried again before use, thereby greatly increasing its cost to the consumer.
In an attempt to prevent the humidification of natural gas by contact with such brines or sediments in such caverns, the surface of the brine was coated with a heavy mineral oil. Such a procedure, however, proved not to be effective, because, in many cases, the higher-boiling hydrocarbons, such as propane and butane, which are present in natural gas and which, under the pressure prevailing in the cavern, are in contact with the surface of the oil layer, dilute the oil layer, and render it ineffective as a separating layer or barrier.
Solidification of the brine with a hydraulic cement is not possible since the cement must be mixed together mechanically with the brine and this is not possible in such subterranean gas-storage caverns which do not have shafts through which tools or workmen can be moved.